Method of manufacturing a display screen

ABSTRACT

An improved method of manufacturing a display screen for a cathode tube in which a coating of a material such as phosphor is provided on the back surface of the display screen and more particularly on the metallic backing of the display screen. This is accomplished by subjecting the metallic coated screen to a suitable vapor until the screen is saturated with vapor and then depositing the phosphor onto the back surface of the metallic backing layer by suitable screening techniques such as settling. The resulting structure is comprised of two phosphor layers with a metallic barrier sandwiched between the phosphor layers.

United States Patent [19] Phillips METHOD OF MANUFACTURING A DISPLAY SCREEN [75] Inventor: Donald M. Phillips, Cayuta, N.Y.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

22 Filed: July 26,1972

211 Appl. No.: 275,388

[52] [1.8. Cl 117/211, 117/33.5 C, 1l7/33.5 CP, l17/33.5 CM, 117/33.5 CS, 117/213,

[51] Int. Cl. H05b 33 /00, HOSb 33/28 [58] Field of Search 117/211, 213, 217, 227, 117/63, 230, 33.5 CF, 33.5 C, 33.5 CM, 33.5

CS; 313/92 R, 92 PH, 65 A [56] References Cited UNITED STATES PATENTS 2,316,041 4/1943 Armentrout 117/63 3,314,871 4/1967 Heck l17/33.5 CP 3,317,337 5/1967 Saulnier ll7/33.5 CP 3,347,693 10/1967 Wendland l17/33.5 CP

[ June 25, 1974 Primary Examiner-Leon D. Rosdol Assistant Examiner-Michael F. Esposito Attorney, Agent, or Firm-W. G. Sutcliff [57] ABSTRACT An improved method of manufacturing a display screen for a cathode tube in which a coating of a material such as phosphor is provided on the back surface of the display screen and more particularly on the metallic backing of the display screen. This is accomplished by subjecting the metallic coated screen to a suitable vapor until the screen is saturated with vapor and then depositing the phosphor onto the back surface of the metallic backing layer by suitable screening techniques such as settling. The resulting structure is comprised of two phosphor layers with a metallic barrier sandwiched between the phosphor layers.

9 Claims, 3 Drawing Figures DRY PHOSPHOR LAYER I6 DEPOSIT ORGANIC FILM ON LAYER I6 DEPOSIT METALLIC LAYER I8 ON ORGANIC FILM BAKE 30 MIN.

AT 425C SATURATE SCREEN WITH VAPOR OF WATER 81 ALCOHOL DEPOSIT PHOSPHOR LAYER 2O SEAL, EXHAUST 8t BAKE TUBE ,PATIENTEUJIUNZSIWI 3.819.409

DEPOSIT PHOSPHOR LAYER I6 ON FACEPLATE I4 DRY PHOSPHOR LAYER I6 DEPOSIT ORGANIC FILM ON LAYER I6 DEPOSIT METALLIC LAYER l8 ON ORGANIC FILM BAKE 30 MIN.

AT 4259s SATURATE SCREEN WITH VAPOR OF WATER SI ALCOHOL DEPOSIT PHOSPHOR LAYER 20 SEAL, EXHAUST8I BAKE TUBE METHOD OF MANUFACTURING A DISPLAY SCREEN BACKGROUND OF THE INVENTION This invention is directed to a method of providing a coating of material such as phosphor on the metallic backing, such as aluminum, of a display screen in a cathode ray tube. One particular application of the invention is to a cathode ray tube wherein a first phosphor layer is provided on the faceplate of a cathode ray tube with an aluminum backing layer. The first phosphor layer may be viewed through the faceplate in response to electron excitation of the first phosphor layer. A second phosphor layer is provided on the backing layer for providing emission in response to electron bombardment of a different color which may be viewed through a back window of the cathode ray tube. The first phosphor layer may be referred to as front emission which may be of a green or yellow color for best eye visibility while the second phosphor layer may be referred to as rear emission and emit in the blue or UV region and adaptable for exposure of films.

A cascade type structure has been used in such a tube. Two layers are settled in sequence to the proper thickness required to obtain the desired emission colors. The screen, however, when viewed from the front will emit a' color mixture containing the combined wavelength of the front and rear phosphor layers. Moreover, due to the requirement that the rear screen be projected to the rear of the tube, the aluminum backing may not be used thereon. The aluminum backing improved output by providing reflection for the light emitted by a phosphor screen. In the absence of the aluminum layer substantially light output from both the front and rear phosphor screen is lost.

This problem can be solved by forming an aluminum layer between the front and rear screens. In this manner, full advantage of the aluminum backing can be obtained with a maximum light output both from the front and the rear screens. This also permits greater latitude in the selection of phosphors for the front screen and a lessening of the somewhat critical screen weight factor. Fabrication of such devices have been found difficult because of the sensitivity of'aluminum film to water or solvents. The sensitivity of the aluminum to the water or solvents results in formation of blisters and wrinkles in the aluminum film in the final product. The aluminum film peels away from the screen when subjected to processing required to form and process the rear screen. It is to this specific problem that this invention is directed and more generally to an improved method of deposition of a coating of material on the back surface of a metallic coated screen without affecting the metallic film.

SUMMARY OF THE INVENTION This invention describes a method of fabricating a display screen wherein a front emission phosphor layer is provided with a metallic backing thereon and a coating of material such as phosphor is provided on the metallic backing to provide emission to the rear. This is accomplished by saturating the metallic backed front phosphor with a suitable vapor such as water and alcohol prior to a deposition of the rear phosphor.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be had to the preferred embodiment, exemplary of the invention, shown in the accompanying drawings, in which:

FIG. 1 is a perspective view partially in section of one form of cathode ray tube in which the present invention is particularly applicable;

FIG. 2 is a flow diagram of steps in the formation of the cathode ray tube screen in accordance with the invention; and

FIG. 3 is a view of apparatus used in the practice of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A cathode ray display tube is illustrated in FIG. I. The tube includes an evacuated envelope 10 having a body portion 12. A front faceplate l4 closes one end of the body portion 12. A screen assembly 21 is provided on the inner surface of the faceplate 12. The screen assembly comprises a front phosphor layer 16 of an electron responsive material that is provided on the inner surface of the faceplate 14. A suitable phosphor is zinc cadmium sulfide activated with copper. This phosphor emits in the visible region portion. The faceplate l4 may be of glass which is transmissive to the radiation generated by the front screen 16. A metallic coating 18 of a suitable electrical conductive material such as aluminum is provided on the rear surface of the front screen 16 and has a thickness of about 1,000 A. The thickness of the coating 18 is normally about 600 to 1,500 A. The coating 18 is substantially opaque to the radiation generated by the front screen 16 and reflects the radiation from the front screen 16. The coating also provides an electrical conductive electrode for the screen 21. A rear screen 20 of a suitable phosphor material such as zinc sulfide activated with silver which emits in the blue portion of the visible region is provided on the rear surface of the aluminum layer 18.

An electron gun 22 is provided within an extension neck portion 24 from the body portion 12 of the envelope 10. The electron gun 22 is provided with suitable potential and deflection means to scan a raster over the rear surface of the screen assembly 21. The potential of the electron beam generated by the electron gun 22 is such as to penetrate through the layers 20, 18 and into the layer 16 so as to excite both the rear and front screens 20 and 16. A rear view window 26 is also provided in the envelope 10 so that a camera or other device may be provided to view the rear screen 20 and record the light image generated thereon by the electron beam generated by the electron gun 22. The front screen 16 emits light to the front and may be observed by a viewer.

FIG. 2 illustrates the steps in the fabrication of the screen assembly 21. The front screen 16 is deposited on the faceplate 14 by any suitable technique such as providing a layer of a suitable liquid such as water and then depositing the phosphor by allowing the phosphor to settle through the liquid cushion onto the inner surface of the faceplate 14. The liquid is then removed and the phosphor coating is dried with dry air. The next step in the manufacture is to provide an organic film on the phosphor layer 16 of a suitable material such as an acrylic base lacquer and then deposit the aluminum layer 18 by a suitable process such as evaporation. The layer 18 is a porous type deposit. The screen is next baked in a lehr furnace for approximtaely 30 minutes The next step in the fabrication of the screen assembly 21 is the deposition of the layer 20. The deposition of the layer is accomplished by first subjecting the interior of the bulb to a vapor of deionized water and alcohol such as illustrated in FIG. 3. The water and alcohol is mixed in a ratio of 1:2 and brought to its boiling point and held to a slow boil about 90 C and the vapors introduced into the bulb until the entire screen 21 is saturated. The length of time is about 1 minute and depends on bulb size and distance of jet orifice to screen. Saturation can be recognized by a darkening of the screen color. A suitable alcohol an ethanol such as SDA-3A which may be purchased from Allied Chemical. lsoproponol may also be used. It was found that the vapors of water or alcohol alone did not prevent blistering, but the mixture was completely successful. After the saturation step, the rear screen 20 is deposited by a suitable process such as that previously described with regard to the screen 16. It is important in this operation that the screen 21 not be allowed to dry out prior to the deposition of the layer 20. One process is to cover the screen with deionized water until the rear screen 20 is applied by normal settling techniques. After the phosphor layer 20 has been settled, the phosphor layer 20 is dired by standard dry air flow technique. Another air bake may often be desirable at this stage prior to sealing and exhausting. Air bake would generally be about 30 minutes at 425 C. The envelope is then sealed and exhausted. The tube is baked for H2 hour at 420 C during this process.

It is found by this manner of manufacture that the aluminum layer 18 does not exhibit the undesirable properties of previous structures wherein there was formation of blisters or wrinkles in the aluminum film after the manufacturing process.

I claim as my invention:

1. The method of forming a screen structure for a cathode ray tube on a substrate of transparent material, said method comprising the steps of: depositing a phosphor coating on said substrate, depositing a volatilizable organic film on said phosphor coating, depositing a porous metallic film on said organic film, said porous metallic film being sufficiently thin to be permeable to electrons wherein said metallic film is selected from the group consisting of aluminum and silver, heating said screen to remove said volatilizable organic film, saturating said phosphor screen and said metallic film with an alcohol containing aqueous solution, and then depositing an electron responsive coating on said saturated metallic film, and drying and heating said screen to volatilize said alcohol containing aqueous solution.

2. The method set forth in claim 1 in which said saturation is provided by boiling a mixture of water and alcohol and subjecting said screen to the vapor from said boiling mixture.

3. The method set forth in claim 2 in which the ratio of water to alcohol is about 1:2.

4. The method set forth in claim 2 in which said alcohol is ethanol.

5. The method set forth in claim 1 in which said electron responsive coating is a phosphor material different from that deposited on said transparent substrate.

6. The method set forth in claim 1 in which said metallic film is deposited by evaporation.

7. The method set forth in claim 6 in which said metallic film is comprised of aluminum.

, 8. The method of forming a multi-layer luminescent screen upon a light transmissive substrate, wherein a thin porous metallic layer is disposed between phosphor layers, which method comprises: depositing a phosphor coating on said substrate, depositing a readily volatilizable organic film on said phosphor coating, depositing a thin porous metallic film on said organic film wherein said metallic film is selected from the group consisting of aluminum and silver, heating said screen to remove said volatilizable organic film, saturating said metallic film with an alcohol containing aqueous solution, and depositing another phosphor coating on said saturable metallic film, and drying and heating said multi-layer luminescent screen to volatilize said alcohol containing aqueous solution.

9. The method set forth in claim 8, wherein said saturation is provided by boiling a mixture of water and alcohol and subjecting said metallic film to the vapor from said boiling mixture. 

2. The method set forth in claim 1 in which said saturation is provided by boiling a mixture of water and alcohol and subjecting said screen to the vapor from said boiling mixture.
 3. The method set forth in claim 2 in which the ratio of water to alcohol is about 1:2.
 4. The method set forth in claim 2 in which said alcohol is ethanol.
 5. The method set forth in claim 1 in which said electron responsive coating is a phosphor material different from that deposited on said transparent substrate.
 6. The method set forth in claim 1 in which said metallic film is deposited by evaporation.
 7. The method set forth in claim 6 in which said metallic film is comprised of aluminum.
 8. The method of forming a multi-layer luminescent screen upon a light transmissive substrate, wherein a thin porous metallic layer is disposed between phosphoR layers, which method comprises: depositing a phosphor coating on said substrate, depositing a readily volatilizable organic film on said phosphor coating, depositing a thin porous metallic film on said organic film wherein said metallic film is selected from the group consisting of aluminum and silver, heating said screen to remove said volatilizable organic film, saturating said metallic film with an alcohol containing aqueous solution, and depositing another phosphor coating on said saturable metallic film, and drying and heating said multi-layer luminescent screen to volatilize said alcohol containing aqueous solution.
 9. The method set forth in claim 8, wherein said saturation is provided by boiling a mixture of water and alcohol and subjecting said metallic film to the vapor from said boiling mixture. 